The present invention relates to optical filters, and more particularly, to tunable Fabry-Perot optical resonators, filters and lasers constructed therefrom.
Tunable optical resonators are utilized in optical communication systems and in the construction of lasers. Optical filters and lasers based on Fabry-Perot resonators can be constructed using microelectromechanical machining (MEM) techniques, and hence, can, in principle, provide an economically attractive tunable filter or tunable laser. In such devices, a Fabry-Perot resonator cavity is formed between two mirrors. One of these mirrors is flat and located on a semiconductor substrate. The other mirror may be curved and is suspended on a number of micro-mechanical cantilevers. Application of a tuning voltage between the cantilevers and the substrate causes the suspended mirror to move towards the fixed mirror on the substrate, thereby reducing the spacing between the two mirrors of the Fabry-Perot resonator. Since the filter""s bandpass frequency is determined by the mirror spacing, a reduction in spacing between the two mirrors causes the resonant optical frequency of the cavity to increase. The shift in the resonant frequency enables the device to be used directly as a tunable bandpass filter. If an optically-pumped or electrically-pumped optical gain medium (active region) is placed in the cavity, the device becomes a tunable laser, with the lasing wavelength controlled by the resonant frequency of the Fabry-Perot cavity.
The need to provide a tuning voltage limits or complicates the use of such cavities. For example, the filter must be provided with an electrical power source and feedback circuitry to provide the correct tuning voltage. The tuning voltages are typically in the range of tens of volts. Such voltage levels are outside the usual control voltages on standard integrated circuits, and hence, the inclusion of this non-optical circuitry increases the cost and complexity of the devices.
Broadly, it is the object of the present invention to provide an improved MEM Fabry-Perot resonator.
It is a further object of the present invention to provide a MEM Fabry-Perot resonator that can be tuned via an optical signal without requiring that signal to be converted to an electrical control signal.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is a tunable optical resonator whose resonance frequency is determined by a light signal introduced into the resonator. The resonator includes an optical cavity having a first mirror and a second mirror. The first mirror and second mirror are supported relative to one another such that the distance between the first and second mirrors may be altered by applying a force to said second mirror thereby altering the resonance frequency of said cavity. The resonator includes a light input port for receiving a tuning light signal, and an optional light signal generator for generating the tuning light source. The tuning light signal is introduced into the optical cavity such that the tuning light signal is reflected between the first and second mirrors. In the absence of the tuning light signal, the resonator has a resonance characterized by a resonance response curve centered at xcex0. The tuning light signal has a wavelength xcex1 within said resonance response curve and sufficient power to cause said resonance response curve to shift such that the resonance response curve is now centered at xcex2, where xcex2 greater than xcex1. In one embodiment of the invention, a circuit for monitoring the light leaving the resonator is utilized to control the wavelength and/or amplitude of the tuning light signal such that the light leaving the resonator has a predetermined wavelength.